REBUILDING AN OLD OS FX46 AERO ENGINE

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I enjoy fiddling about with mechanical objects generally, so model aero engines are a prime target for me, old two strokes don't cost that much, if you mess up! so here are a few of my observations:
I obtained a worn out OSFX46 from a friend for the princely sum of a network card for his PC! This engine was a bit past its sell by date to say the least, the cylinder head was damaged & the piston & liner were positively corrugated!
I looked on the excellent "Just Engines" website & they advertise a "OSFX46 short engine". The price is reasonable enough at approx £45.00 (inc postage) so I sent off for one, nothing to lose but £45.00 methinks. I may be wrong here, but what I received appeared to be a "Super Custom 46" with the "SC" name milled off the crankcase. I fitted my OS carburettor & backplate from the OSFX46 & bolted the engine into a "Weston Cougar" funflyer to have a play with it. I then sent off to "Just Engines" for a "Genesis" throttle pipe. This duly arrived the next day & I bolted that to the engine, using 5 minute epoxy as a sealant on the exhaust port.
The engine was very tight over TDC, which is good on an "ABC" (Aluminium piston with Brass Chomed liner) two stoke engine. Using my own fuel mix (see below) The engine started well & I ran it in using the usual technique for "ABC" engines, that is, get the engine's piston & liner up to temperature quickly, so I didn't run it very rich etc, in fact I "thrashed" it a bit if I am honest! After a couple of tankfuls of fuel the engine ran very smoothly - I adjusted the "bottom end" mixture needle, & after 4 tankfuls through it, I clocked 12,000 RPM on a 12 x 5 prop - very good - only just 82 Db I think though! 12,000 RPM is a little more than my usual engine propeller configuration allows, owing to the 82 Db noise regulations at the DMAC flying site.
Anyway, I took the model down to our flying field & the performance was amazing in the "Cougar", which had previously been fitted with a very good "Irvine40 " with standard silencer. But now ..... Take off in 4 -5 feet, straight up - vertical - as fast as most models fly level! prop hanging on quarter throttle, great idling reliability - Impressed!
At this point I must mention that I modify my fuel:
I always buy a normal gallon of "Superglo" or similar with 5 % nitromethane , I divide this into 3 equal parts in other 1 gallon fuel containers, then top up the containers with neat methanol, shaking well, so I have 2 thirds neat methanol, one third standard fuel in each gallon container. I run all my engines (mainly Lasers & a couple of OS) on this mixture with absolutely no ill effects. The "bottom end" of the carburettors on my engines need leaning out a bit, as does the main needle. The benefits are: Much less oil residue on my models, smoother running, more reliable engines, better fuel economy - need I say more? The "purists" may moan about this, but it works for me. Years ago, with my "Webra Speed60" & "Speed40" size two strokes doing 15,000 + RPM (in a less noise conscious world), I always used standard fuel. But even in the early 1980's I used to run my OSFS60 & OSFS40 (four strokes) on this "diluted" fuel mix with no ill effects at all!
Back to the engine:
One thing bothered me - the milled off "SC" casting on the crankcase looked tacky, & people kept asking "what's that engine?" So as soon as I got chance, I dismantled the engine to have a look at its internal components & quality, & see about transferring the internal components & cylinder head into my OSFX46 crankcase.
A COMPARISON:
CRANKCASE & CYLINDER HEAD: near enough same visible quality to the OSFX46.
PISTON & LINER: slightly different, shinier, & well made.
CRANKSHAFT: not so good - inlet port physically smaller, crankpin drilling too long, location hole being drilled through into the ball race location area, not a problem though. According to my digital micrometer, the crankpin was machined smaller in diameter than the crankpin on the old OSFX46, & the new con rod is a better fit on the old OS crankpin - not tight - just right.
BEARINGS: I didn't like these much, the front bearing was thicker than the OS, but the rear main bearing had a very thin plastic ball retaining collar which I personally did not like, I felt that this was not sufficient to hold the balls in position seurely over a long period . I removed it, played with it, and destroyed it very easily!
SOLUTION: I bought a new rear main bearing from a local supplier "Spen Bearings" - Japanese manufacture, high quality & it only cost me £3.00! I thoroughy cleaned, lubricated & re-assembled the OSFX46 using the piston, conrod, liner, cylinder head & nice shiny prop driver from the "Just Engines" short engine.
RESULT: I NOW HAVE AN ENGINE WHICH HAS "OSFX" CAST ON THE SIDE OF THE CRANKCASE & SEEMS TO RUN JUST AS WELL AS THE "SHORT ENGINE" DID.
No criticism at all is levelled at "Just Engines" I received what I expected to receive - a "clone" engine at "clone" prices & besides, it ran very well indeed. I can highly recommend their services. Their mail order service is very efficient as well. Who knows I might even rebuild the other engine too! - I wonder what the new OS AX range are like?

 

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